Solar PV, Immersion diverter and EV Charging

[JamesPa]

I have solar PV with an immersion diverter.  I am about to buy an electric car.  In my ideal world, when it sunny, the PV would first heat the DHW then charge the car.

 

I know this can be done if you buy the immersion diverter and ev charger box from the same company.  I also know that many EV charger boxes can accept a CT input to allow them to 'soak up' extra power.   However the immersion diverter is already doing that, and the two will (presumably) simply fight each other.

 

Does anyone know a way to get them to play nicely other than by both coming from the same manufacturer?

[JohnMo]

Can't you just put the CT clamps sequential, PV first then car?

[SteamyTea]

Why don't you play the number's game.

Have a look at your past PV generation, find the period, that on average, has the greatest generation, then just charge the car during those times.

Heat the water either side of those times as I suspect that the water will take less current and react faster to changes.

[RichardL]

Is your EV sitting in the drive when the sun is shining?
I found it easier to charge the car on the known off peak overnight, along with water heating and let the PV/Batteries time shift some of that off peak to run the house.

Granted it depends how much PV you have and if the car is there when the sun is shining vs. a work destination.

Not yet bought into the over complex cloud solutions/integration.

[SteamyTea]

41 minutes ago, RichardL said:

Is your EV sitting in the drive when the sun is shining

Good point. 

42 minutes ago, RichardL said:

let the PV/Batteries time shift some of that off peak to run the house

If they have charge in them, they will contribute to EV and DHW charging, so may need to be locked out, or set to charge at the same time.

All becomes a bit of a balancing act.

[joth]

1 hour ago, JohnMo said:

Can't you just put the CT clamps sequential, PV first then car?

Not quite unless you're lucky enough to have the EV charger on a separate CU downstream of the PV + immersion CU.

If it's all into one CU you* can play clever tricks by folding the immersion diverter cable (for example) through the EV charger's CT clamp in addition to the meter tails, so the EV sees the sum of what's being imported and what's going into the immersion, and will only start charging when the sum of both crosses below zero

e.g. https://greening.me.uk/2020/12/05/current-clamps/

 

* - doing it in a regs compliant way is tricky as you need to do it all inside the CU, and unless you have a large / 3ph DB there tends to be a lack of space in UK CUs.

 

 

[RichardL]

48 minutes ago, SteamyTea said:

or set to charge at the same time.

This - for now... If the batteries are charging they're not discharging and if yesterday was sunny then overnight they'll have some residual to reduce the overnight top up.
Keeping an eye on the overall draw from the grid with batteries/immersion and car all pulling at the same time.

I still think a time of day based system is simpler than relying on layers external infrastructure/cloud to be up and talking to each other,

You just have to look at solis inverter forums for the regular changes/breaks and downtime on their offering, I suspect others are similar or at least out of the consumer's control?

I can only offer it IS possible to keep it simple - for the moment.

[JamesPa]

Thanks everyone.  No batteries and yes the ev is (sometimes) on the drive when sun is shining.  I'm certainly not doing anything involving the cloud, too complex and low able to fail, but folding back wires gives me some possible ideas.  The immersion is on a separate circuit so perhaps I can fold that into the ct clamp outside the cu to do the sum.

 

I also need to do the calculation on daytime export tariff vs nighttime import tariff, it maybe it's not worthwhile trying to play this game, and instead just export during the day and import for ev charging during the night (which is a lot simpler!).

 

The diverter has a second load port which switches on when the primary load is satisfied.  If EV chargers had an 'enable' input then this could, in principle, be used instead.  However so far as I know they don't, and I'm not comfortable switching a 45A load on a relay.

[joth]

2 hours ago, JamesPa said:

folding back wires gives me some possible ideas.  The immersion is on a separate circuit so perhaps I can fold that into the ct clamp outside the cu to do the sum.

Note only one core should go through the CT, and in the correct direction. If you put the whole cable through the two cores cancel each other out and you'll always get a zero current reading 

[JamesPa]

12 hours ago, joth said:

Note only one core should go through the CT, and in the correct direction. If you put the whole cable through the two cores cancel each other out and you'll always get a zero current reading 

Thanks.  I was aware of this but thanks anyway.

 

I'm wondering also about switching the charger ct in and out of circuit, which would be a safer option.  If I use the secondary output from the immersion diverter as the signal source, the diverter should sort out the prioritization I think.

[Alan Ambrose]

Note that open CT’s are not usually a good thing.

 

>>> I know this can be done if you buy the immersion diverter and ev charger box from the same company.

 

Unless you’ll enjoy figuring a non-standard solution which nobody else coming along later will really understand or you can’t accomplish something like your goal by other means (timing etc) … then maybe you’ve identified the best long term solution already?